Depth sounder repeater structure and method

• US 4,323,992 A
• Filed: 11/01/1979
• Issued: 04/06/1982
• Est. Priority Date: 01/02/1976
• Status: Expired due to Term

• Current Assignee: Leo W. Tobin Jr
• Original Assignee: Leo W. Tobin Jr
• Inventors: Tobin, Leo W. Jr.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US06/090,177
• Time in Patent Office: 887 Days
• Field of Search: 367/108, 367/112, 367/114
• US Class Current: 367/108
• CPC Class Codes: G01S 15/14 wherein a voltage or current pulse is initiated and terminated in accordance respectively with the pulse transmission and echo reception

Abstract

A depth sounder repeater providing a remote display of the depth of a body of water digitally or by meter movement, a depth alarm, a lost echo signal, and a meter scale expansion for shallow depth display in conjunction with a ship'"'"'s sonar, display of "alarm depth" while setting. The depth display may be digital or analog and multiple displays are possible as required. The depth sounder repeater includes a signal processor for providing signals initiated with the main ultrasonic pulse transmission from the ship'"'"'s sonar and terminated with the receipt of the first echo of the corresponding main transmitted pulses. The signal processor signals may then be used to initiate and terminate production of a train of clock pulse signals which are counted to provide a digital depth display, or alternatively the signal processor signal may be integrated in analog meter display apparatus.

Claims

1. A depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance, comprising a signal receiving circuit including a first inverter for receiving the main transmitted sonar pulses, a first multivibrator for receiving the output signal from the first inverter and the echo pulses for producing a square wave output signal, the pulse width of which is representative of the time between the main transmitted sonar pulse and the first corresponding echo signal, a first differentiator circuit for receiving the square wave signal and producing a positive and a negative going trigger signal in response thereto, a display timing circuit including a one-shot multivibrator for receiving the negative going trigger signal representative of the time of receipt of the echo signal operable to produce a second square wave output signal in response to the negative going trigger signal, and a second inverter circuit for inverting the second square wave signal, a differentiator connected to the second inverter for differentiating the inverted square wave output of the one-shot multivibrator to provide a display timing circuit trigger signal, a one and only one circuit including a third and fourth multivibrator, the third multivibrator being connected to the display timing circuit for receiving the display timing circuit trigger signal and operable on receipt of the display timing circuit trigger signal to prepare the fourth multivibrator to produce an output signal in response to the next following main transmitted sonar pulse through the first inverter, said fourth multivibrator being connected to receive the output signals from the first inverter and also being connected to receive echo input signals from the first differentiator operable to turn the fourth multivibrator off, said fourth multivibrator being operable on turning on to reset the third multivibrator so that the third multivibrator will not again prepare the fourth multivibrator to produce an output signal until the receipt of a further display timing circuit trigger signal, a timing oscillator, said fourth multivibrator being also operable to actuate the timing oscillator to produce periodic electric signals during the time the fourth multivibrator produces an output signal, and a display circuit including a plurality of binary coded decimal counters connected to receive the output impulses of the timing oscillator and to receive the display timing circuit trigger signal for resetting of the binary coded decimal counters, binary decoder structure connected to the binary coded decimal counters for decoding the binary coded decimal counter signals subsequent to the timing oscillator being shut off and a binary display circuit connected to the binary decoder circuits for providing a binary display of the distance between the sonar and the object which returned the first echo signal as represented by the electrical impulses from the timing oscillator in the time between a main sonar transmitted pulse and the corresponding first received echo pulse.

2. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency electrical energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance, comprising signal receiving circuit means for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse of the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse and further including a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth, said depth alarm circuit comprising a one-shot multivibrator connected to the input circuit for producing an output depth alarm pedestal, means for varying the depth alarm pedestal, a multivibrator for receiving the pedestal and a differentiated signal representative of the depth indicated by the echo signal from the input circuit and for providing an output when the depth indicated by the echo signal is less than the depth alarm pedestal.

3. Depth sounder repeater structure for use in conjunction with shipboard sonar producing a main pulse and receiving echo pulses from distant underwater objects, comprising an input circuit including a first flip-flop, a detector connected to the shipboard sonar for receiving transmitted main sonar pulses and detecting the envelope of the pulses, a main Schmidt trigger circuit connected to receive the output of the detector to provide a first input to the flip-flop, a first inverter connected to receive the echo pulses of the transmitted main sonar pulses, an echo Schmidt trigger circuit connected to the first inverter and to the multivibrator to provide a second input to the first flip-flop whereby the output of the first flip-flop is a square wave signal representative of the distance traveled by a main sonar pulse to a first reflecting underwater object, a buffer and inverter connected to the first flip-flop to receive the square wave output signal therefrom, and AND gate receiving the output of the buffer and inverter on one input thereto, variable, first and second resistors connected in series and connected to the AND circuit for receiving the output thereof, and an integrating indicator connected to receive the signal from the AND gate through the first and second resistors, a first switch having a first portion connected in one position to bypass the second resistor, a first capacitor, said first switch, first portion being operable in said one position to bypass the second resistor, and in another position to connect the first capacitor in parallel with the integrating meter, a lost echo circuit connected between the buffer and inverter and another input to the AND circuit comprising a second capacitor and third resistor connected in series, a diode connected in parallel with the third resistor, a first transistor having a base, emitter and collector, said base being connected to the first resistor of the end thereof away from the second capacitor, a fourt resistor connected at one end to the emitter of the transistor, and connected between the second capacitor and third resistor at the other end, a third capacitor connected across the emitter and collector of the first transistor, a first one-shot multivibrator connected between the other input to the AND gate and the emitter of the transistor, a fifth resistor, and a light emitting diode connected between a source of power therefor and the other input to the AND gate through the fifth resistor, a scale expansion circuit including a second one-shot multivibrator connected to the output of the main Schmidt trigger circuit, a variable sixth resistor and a fourth capacitor connected in series connected to the one-shot multivibrator for determining the time of timing out of the second one-shot multivibrator, a second inverter having an input connected to the output of the second one-shot multivibrator and a second portion of the first switch operable in one position thereof to connect the output of the second inverter to the flip-flop and in the other position thereof to connect the flip-flop to ground, and a depth alarm circuit including a third one-shot multivibrator connected to the main Schmidt trigger circuit and through a variable seventh resistor and across a fifth capacitor to a power source operable to time out in accordance with the values of the seventh resistor and fifth capacitor, a second flip-flop for receiving the output of the depth alarm third one-shot multivibrator and for receiving the output of the first flip-flop of the input circuit through a sixth capacitor and across a parallel connected eighth resistor and seventh capacitor, a depth alarm second transistor having a base connected through a ninth resistor to the output of the depth alarm second flip-flop and an emitter-collector circuit connected in series with an alarm and an alarm switch, and a light emitting diode connected in parallel with the ninth resistor and the base emitter circuit of the second transistor.

4. Structure as set forth in claim 3, and further including an eigth capacitor and a variable tenth resistor in an input circuit to the first inverter, and a second switch for switching the input to the first inverter between the echo signal of the main sonar and the output signal of the third one-shot multivibrator of the depth alarm circuit for providing an accurate indication of setting of the depth alarm circuit.

5. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency electrical energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse and comprising a scale expansion circuit including a one-shot multivibrator connected to the input circuit to receive a signal representative of the main sonar pulses, an inverter circuit connected to the one-shot multivibrator portion to invert the output of the one-shot multivibrator, and means for feeding the inverted signal from the one-shot multivibrator to the input circuit after a predetermined selectable time representative of the predetermined depth, and means within the input circuit for inhibiting echo signals from passing through the input circuit if the echo signals reflect a depth less than the predetermined depth, and a manually operable switch having portions connected in the scale expanding circuit and portion connected in the output circuit for producing a full scale reading in the output circuit indicating a depth less than the predetermined depth, and for producing full scale reading for depths of the predetermined depth in alternate settings thereof.

6. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency electrical energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse and comprising a scale expansion circuit including a one-shot multivibrator connected to the input circuit to receive a signal representative of the main sonar pulses, an inverter circuit connected to the one-shot multivibrator portion to invert the output of the one-shot multivibrator, and means for feeding the inverted signal from the one-shot multivibrator to the input circuit after a predetermined selectable time representative of the predetermined depth, and means within the input circuit for inhibiting echo signals from passing through the input circuit if the echo signals reflect a depth less than the predetermined depth, and a manually operable switch having portions connected in the scale expanding circuit and portions connected in the output circuit for producing a full scale reading in the output circuit indicating a depth less than the predetermined depth, and for producing full scale reading for depths of the predetermined depth in alternate settings thereof, and further including a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth.

7. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency electrical energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse and comprising a one-shot multivibrator connected to the input circuit for producing an output depth alarm pedestal, means for varying the depth alarm pedestal, a multivibrator for receiving the pedestal and a differentiated signal representative of the depth indicated by the echo signal from the input circuit and for providing an output when the depth indicated by the echo signal is less than the depth alarm pedestal.

8. Depth sounder repeated structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, a timing oscillator for producing electrical impulses at a selected rate during the time it is turned on, means operable between the signal receiving means and the timing oscillator for insuring that one and only one main sonar pulse and the first echo from the one main sonar pulse turns the oscillator on and off respectively including a first multivibrator for preparing a second multivibrator to receive a main transmission pulse and to produce an output responsive thereto for turning on the timing oscillator, in response to the first echo signal, and a second multivibrator for receiving the main transmitted signal operable when prepared to provide an output signal to the timing oscillator on receipt of the main transmitted signal and to subsequently cut off the output signal to the timing oscillator in response to the receipt of the first echo signal of the corresponding main transmitted signal and to provide a signal for returning the first multivibrator to a state wherein it will not prepare the second multivibrator to receive another main transmission pulse, and display means connected to the timing oscillator for displaying the depth indicated by the time between the one main sonar pulse and the first echo thereof as represented by the number of electrical impulses produced by the timing oscillator in the time between the one main pulse and the first echo thereof.

9. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, a timing oscillator for producing electrical impulses at a selected rate during the time it is turned on, means operable between the signal receiving means and the timing oscillator for insuring that one and only one main sonar pulse and the first echo from the one main sonar pulse turns the timing oscillator on and off respectively, display means connected to the timing oscillator for displaying the depth indicated by the time between the one main sonar pulse and the first echo thereof as represented by the number of electrical impulses produced by the timing oscillator in the time between the one main pulse and the first echo thereof and a display timing circuit operably associated with the signal receiving circuit means, the one and only one circuit and the display circuit including a one-shot multivibrator for receiving a differentiated square wave signal from the signal input circuit operable in response to the first received echo signal of a main transmitted pulse to produce an output signal, means for inverting the output signal of the one-shot multivibrator and means for differentiating the inverted output signal of the one-shot multivibrator to provide a trigger pulse for actuating the one and only one circuit periodically for limiting the one and only one circuit to selected periodic actuation and to reset the display circuit immediately prior to each actuation of the one and only one circuit.

10. Structure as set forth in claim 9, wherein the means for insuring that one and only one main sonar pulse and the first echo from the one main sonar pulse turns the timing oscillator on and off respectively includes a first multivibrator for preparing a second multivibrator to receive a main transmission pulse and to produce an output responsive thereto fur turning on the timing oscillator, in response to the first echo signal, and a second multivibrator for receiving the main transmitted signal operable when prepared to provide an output signal to the timing oscillator on receipt of the main transmitted signal and to subsequently cut off the output signal to the timing oscillator in response to the receipt of the first echo signal of the corresponding main transmitted signal and to provide a signal for returning the first multivibrator to a state wherein it will not prepare the second multivibrator to receive another main transmission pulse.

11. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse and means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit including an AND gate and a lost echo circuit connected to receive the square wave signal from the input circuit and to provide one input to the AND gate including a one-shot multivibrator and structure connected to the one-shot multivibrator for receiving the square wave pulse from the input circuit and preventing timing out of the one-shot multivibrator on loss of the echo signal, including a differentiating circuit having a capacitor and resistor in series for receiving the square wave pulse from the input circuit, a transistor operable to be turned on on reception of the square wave pulse from the input circuit across the differentiating circuit, and a resistor and capacitor in series between the differentiating circuit and the transistor, the capacitor of which is connected across the emitter collector circuit of the transistor for determining the time of turn on of the transistor and therefore the timing out of the multivibrator, and an indicator light connected to the multivibrator operable to indicate the timing out of the multivibrator and thus the loss of the echo signal from the sonar.

12. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit including an AND gate and a lost echo circuit connected to receive the square wave signal from the input circuit and to provide one input to the AND gate including a one-shot multivibrator and structure connected to the one-shot multivibrator for receiving the square wave pulse from the input circuit and preventing timing out of the one shot multivibrator on loss of the echo signal, including a differentiating circuit having a capacitor and resistor in series for receiving the square wave pulse from the input circuit, a transistor operable to be turned on on reception of the square wave pulse from the input circuit across the differentiating circuit, and a resistor and capacitor in series between the differentiating circuit and the transistor, the capacitor of which is connected across the emitter collector circuit of the transistor for determining the time of turn on of the transistor and therefor the timing out of the multivibrator, and an indicator light connected to the multivibrator operable to indicate the timing out of the multivibrator and thus the loss of the echo signal from the sonar and means operably connected to the input and output circuit for sensing depths below and above a predetermined depth and for manually changing the full scale reading of the output circuit in response to recognition of a predetermined depth.

13. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing tranmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit and means operably connected to the input and output circuits for sensing depths below and above a predetermined depth and for manually changing the full scale reading of the output circuit in response to recognition of a predetermined depth comprises a scale expansion circuit including a one-shot multivibrator connected to the input circuit to receive a signal representative of the main sonar pulses, an inverter circuit connected to the one-shot multivibrator to invert the output of the one-shot multivibrator, and means for feeding the inverted signal from the one-shot multivibrator to the input circuit after a predetermined selectable time representative of the predetermined depth, and means within the input circuit for inhibiting echo signals from passing through the input circuit if the echo signals reflect a depth less than the predetermined depth, and a manually operable switch having portions connected in the scale expanding circuit and portions connected in the output circuit for producing a full scale reading in the output circuit indicating a depth less than the predetermined depth, and for producing full scale reading for a depth above the predetermined depth in alternate settings thereof.

14. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses form distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit including an AND gate and a lost echo circuit connected to receive the square wave signal from the input circuit and to provide one input to the AND gate including a one-shot multivibrator and structure connected to the one-shot multivibrator for receiving the square wave pulse from the input circuit and preventing timing out of the one-shot multivibrator on loss of the echo signal, including a differentiating circuit having a capacitor and resistor in series for receiving the square wave pulse from the input circuit, a transistor operable to be turned on on reception of the square wave pulse from the input circuit across the differentiating circuit, and a resistor and capacitor in series between the differentiating circuit and the transistor, the capacitor of which is connected across the emitter collector circuit of the transistor for determining the time of turn on of the transistor and therefore the timing out of the multivibrator, and an indicator light connected to the multivibrator operable to indicate the timing out of the multivibrator and thus the loss of the echo signal from the sonar, means operably connected to the input and output circuits for sensing depths below and above a predetermined depth and for manually changing the full scale reading of the output circuit in response to recognition of a predetermined depth and further including a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth.

15. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circiuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit, means operably connected to the input and output circuits for sensing depths below and above a predetermined depth and for manually changing the full scale reading of the output circuit in response to recognition of a predetermined depth including a scale expansion circuit including a one-shot multivibrator connected to the input circuit to receive a signal representative of the main sonar pulses, an inverter circit connected to the one-shot multivibrator portion to invert the output of the one-shot multivibrator, and means for feeding the inverted signal from the one-shot multivibrator to the input circuit after a predetermined selectable time representative of the predetermined depth, and means within the input circuit for inhibiting echo signals from passing through the input circuit if the echo signals reflect a depth less than the predetermined depth, and a manually operable switch having portions connected in the scale expanding circuit and portions connected in the output circuit for producing a full scale reading in the output circuit indicating a depth less than the predetermined depth, and for producing a full scale reading for depths of the predetermined depth in alternate settings thereof and a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth.

16. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit, means operably connected to the input and output circuits for sensing depths below and above a predetermined depth and for manually changing the full scale reading of the output circuit in response to recognition of a predetermined depth and a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth including a one-shot multivibrator connected to the input circuit for producing an output depth alarm pedestal, means for varying the depth alarm pedestal, a multivibrator for receiving the pedestal and a differentiated signal representative of the depth indicated by the echo signal from the input circuit and for providing an output when the depth indicated by the echo signal is less than the depth alarm pedestal.

17. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit including an AND gate and a lost echo circuit connected to receive the square wave signal from the input circuit and to provide one input to the AND gate including a one-shot multivibrator and structure connected to the one-shot multivibrator for receiving the square wave pulse from the input circuit and preventing timing out of the one-shot multivibrator on loss of the echo signal, including a differentiating circuit having a capacitor and resistor in series for receiving the square wave pulse from the input circuit, a transistor operable to be turned on on reception of the square wave pulse from the input circuit across the differentiating circuit, and a resistor and capacitor in series between the differentiating circuit and the transistor, the capacitor of which is connected across the emitter collector circuit of the transistor for determining the time of turn on of the transistor and therefore the timing out of the multivibrator, and an indicator light connected to the multivibrator operable to indicate the timing out of the multivibrator and thus the loss of the echo signal from the sonar and a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the echo signal is less than a predetermined selected depth.

18. Depth sounder repeater structure for use in conjunction with shipboard sonar which shipboard sonar produces main transmitted pulses of high frequency energy and receives echo pulses from distant underwater objects the time between which is representative of an underwater distance comprising signal receiving circuit means connected to the shipboard sonar by only four lines for receiving a main sonar pulse and the first echo pulse corresponding thereto and producing a square wave electrical signal having a pulse width representative of the time between the reception of the main sonar pulse and the first echo pulse by the repeater structure, an output circuit for receiving the square wave signal and providing an indication representative of the distance between the sonar and a reflecting object producing the first corresponding echo pulse, means operably connected between the input circuit and output circuit for preventing transmission of square wave pulses from the input circuit to the output circuit when no echo signal is received by the input circuit and a depth alarm circuit connected to the input circuit for providing an alarm when the depth indicated by the cho signal is less than a predetermined selected depth including a one-shot multivibrator connected to the input circuit for producing an output depth alarm pedestal, means for varying the depth alarm pedestal, a multivibrator for receiving the pedestal and a differentiated signal representative of the depth indicated by the echo signal from the input circuit and for providing an output when the depth indicated by the echo signal is less than the depth alarm pedestal.